Three-dimensional (3D) imaging systems are increasingly being used in a wide variety of applications, such as high-speed 3D-imaging systems for advanced driver-assistant systems (ADAS), and high-speed 3D-imaging systems for autonomous navigation. Existing 3D-imaging technologies may, for example, utilize TOF-based range imaging, stereo-vision systems, and/or structured-light techniques.
In a TOF technique, range (or distance) to a 3D object may be resolved based on the known speed of light and by measuring the round-trip time it takes for a laser pulse or a light pulse to travel between a camera and the 3D object. A TOF camera may use a scannerless approach to capture an entire scene with each laser pulse or light pulse. Some examples TOF applications include advanced automotive applications, such as active pedestrian safety or precrash detection based on real time distance images to track movements of humans, objects or other vehicles; interaction with games on video game consoles; and industrial machine vision to classify objects and help robots find, for example, items on a conveyor belt. TOF-based systems that use a single-photon avalanche diode (SPAD) sensor may have low spatial resolution, low fill factor, and high power consumption if a time-to-digital counter (TDC) is placed inside each pixel. Moreover, using a differential time-to-charge converter (DTCC) as part of the sensor may result in a low range accuracy.
Stereoscopic-imaging or stereo-vision systems use two cameras that are displaced horizontally from each other to obtain two differing views of a scene or of a 3D object in the scene. By comparing the two images, relative depth information may be obtained for the 3D object. Stereo vision is highly important in fields, such as robotics, to extract information about the relative position of 3D objects in the vicinity of autonomous systems and robots. Other applications that may use robotic stereoscopic imaging include object recognition in which stereoscopic depth information allows a robotic system to separate occluding image components that the robot may otherwise not be able to distinguish as two separate objects. For example, a robot using stereo vision may not be able to distinguish two objects if one object is in front of a second object, thereby partially or fully hiding the second other object. Three-dimensional stereo displays are also used in entertainment and automated systems.
A structured-light (SL) technique measures a 3D shape of an object by using projected light patterns and an imaging camera. A known pattern of light, such as a grid, horizontal bars or other patterns of parallel stripes, may be projected onto a scene or a 3D object in the scene, and the projected pattern may become deformed or displaced as it strikes the surface of the 3D object. Such a deformation may allow an SL vision system to determine the depth and surface information of the object. That is, projecting a narrow band of light onto a 3D surface may produce a line of illumination that may appear distorted from a perspective that is different from the perspective of the projector. The distortion may be used for a geometric reconstruction of the illuminated surface of the 3D object. SL-based 3D imaging techniques may be used in different applications, such as photographing fingerprints in a 3D scene, inline inspection of components during a production process, and in a health-care environment to obtain live measurements of human body shapes or the micro structures of human skin.